Equis ISSN 2398-2977

Pulmonary: scintigraphy - ventilation and perfusion

Synonym(s): V/Q scintigraphy

Contributor(s): David Marlin, Rachel Murray, Jo Weekes

Introduction

A. Pulmonary perfusion scintigraphy
  • This is a sensitive, non-invasive method of demonstrating pulmonary perfusion.
  • Qualitative and quantitative information can be obtained.
  • Performing a perfusion and ventilation study of the lungs increases the specificity.
    Radiopharmaceutical
  • The radiopharmaceutical used is 99mtechnetium (Tc) human macroaggregated albumin (MAA).
  • The radionuclide 99mTc emits gamma rays only of the energy 140 KeV and has a half-life of 6 h.
  • Radiopharmaceutical dose of 99mTc MAA, 1 MBq/kg.
  • On intravenous injection the 99mTc MAA particles are stopped on first pass through the pulmonary circulation by occluding small branches of the pulmonary artery and capillaries. The resultant distribution of the 99mTc MAA reflects the regional perfusion of the lungs.
  • The occlusion of the vessels lasts approximately 4-8 h, with the 99mTc MAA particles being phagocytosed by the cells of the reticulo-endothelial system.
    B. Pulmonary ventilation scintigraphy
  • This is a sensitive, non-invasive method of demonstrating pulmonary ventilation.
  • Qualitative and quantitative information can be obtained.
  • Performing a ventilation and perfusion study of the lungs increases the specificity of the study.
    Radiopharmaceuticals
  • Gases, pseudogases and aerosols can be used to study lung ventilation. However, radioactive gases provide physiologically ideal agents for representing the distribution of air within the lungs.
  • 81mkrypton (Kr) gas is the agent of choice. It is the daughter product of 81rubidium (Rb) (half-life 4.6 h) and is extracted from the parent by passing humidified air through the 81Rb generator. 81mKr has the following advantages over other radiopharmaceuticals:
    • It is a physiological gas.
    • A short half-life of 13 s, therefore allowing disposal into the atmosphere.
    • Gamma ray energy of 190 keV making it ideal for imaging with conventional gamma camera systems.
    • Low radiation dose.
    • Simultaneous acquisition of perfusion possible due to its different gamma energy to 99mTc.
    • Little crosstalk with 99mTc.
    • Easy to use.
    • Multiple views possible.
    • Good quality images.
  • However, 81mKr has the following disadvantages:
    • It is expensive.
    • ?Short half-life of generator.
    • Limited availability.

    Other radiopharmaceuticals available for pulmonary ventilation imaging
  • 99mTc-diethylenetriaminepentaacetic acid (DTPA) aerosol:
    • 99mTc DTPA particles can be used to image lung ventilation.
    • Particles being significantly larger, behave differently to gases and are therefore distributed differently.
    • Nevertheless, they can be used to give a reasonable representation of the distribution of ventilation if the mean particle size is small enough to ensure alveolar deposition, ie <5 um.
    • 99mTc DTPA is cheap, easy to use and readily available. However, a high quality nebuliser in a shielded lead unit and a suitable scavenging system are required.
    • In addition, simultaneous acquisition of perfusion and ventilation images is not possible, particles are deposited at sites of turbulence and adhere to mucus (which may produce hot spots) and the radiation dose is high.
  • 99mTc Technegas:
    • A pseudogas, which consists of microscopic particles of carbon.
    • Technegas has the advantage in that it is technetium labelled and its distribution within the lung is closer to that of air than aerosols.
    • Its main disadvantage is that the dispensing system and its associated equipment is extremely expensive.
  • 133 Xenon (Xe) gas and 127 xenon (Xe) gas:
    • Both have the disadvantages that image quality is poor when used when used conventional gamma camera systems this is due to the high energy gamma rays emitted by 127Xe (173 and 202 keV) and the low energy gamma emissions from 133Xe.
    • Other disadvantages are the exhaled gas must be trapped and dealt with safely due to their long half-lifes (127Xe - 30 days and 133Xe 5.3 days) and only a single view is possible.

Uses

  • As an aid to diagnosis, prognosis and monitoring response to treatment in pulmonary conditions such as recurrent airway obstruction (RAO)   Lung: recurrent airway obstruction (RAO)    Pulmonary: scintigraphy - ventilation  perfusion  and exercise induced pulmonary hemorrhage (EIPH)   Lung: EIPH (exercise-induced pulmonary hemorrhage)  .
  • Quantifying pulmonary damage following infectious, eg pneumonia, or non-infectious insults.
  • Important roles in future research into pulmonary function, pathological processes and in the development of treatment for respiratory disease.

Advantages

  • Pulmonary scintigraphy is a sensitive non-invasive method of demonstrating the functional status of the lungs, but has a low specificity. If an abnormality in ventilation and or perfusion is demonstrated with pulmonary scintigraphy, further diagnostic modalities must be employed to identify the disease process. However, radiographing the horse's thorax at the time of the study in order to categorize any changes seen in the lung scintigram can increase the specificity of the study.
  • Provides information about regional lung perfusion that is not available from conventional investigations.

Disadvantages

  • Limited availability - specialist centers only.
  • Low specificity - results should be interpreted with clinical examination and other diagnostic techniques.
  • Equipment and radiopharmaceuticals are expensive.

Requirements

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Preparation

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Procedure

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Aftercare

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Further Reading

Publications

Refereed papers

  • Recent references from PubMed and VetMedResource.
  • Votion D M, Coghe J D & Lekeux P M (2001) Comparison of deposition images obtained by use of an ultrafine 99m-technetium-labeled carbon dry aerosol with ventilation images obtained by use of 81m-krypton gas for evaluation of pulmonary dysfunction in calves. Am J Vet Res 62 (12), 1881-1886 PubMed.
  • Coghe J, Votion D & Lekeux P (2000) Comparison between radioactive aerosol, technegas and krypton for ventilation imaging in healthy calves. Vet J 160 (1), 25-32 PubMed.
  • Votion D M, Roberts C A, Marlin D J & Lekeux P M (1999) Feasibility of scintigraphy in exercise-induced pulmonary haemorrhage detection and quantification - preliminary studies. Equine Vet J Suppl 30, 137-142 PubMed.
  • Votion D, Vandenput S, Duvivier H, Art T & Lekeux P (1997) Analysis of equine scintigraphical lung images. Vet J 153 (1), 49-61 PubMed.
  • Votion D, Ghafir Y, Munsters K, Duvivier D H, Art T & Lekeux P (1997) Aerosol deposition in equine lungs following ultrasonic nebulisation versus jet aerosol delivery system. Equine Vet J 29 (5), 388-393 PubMed.

Other sources of information

  • Sharp P F, Gemmell H G & Smith F W (1989)Practical Nuclear Medicine.Oxford University Press.


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